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Applied Physics Letters

Adjustable entanglement enhancement via approaching to higher-order exceptional points in non-Hermitian network system

Yu Wang, Chengtian Liang, Lijiong Shen, Yang Xiao, Qi-Ping Su, Shuai Liu, Yi-Hao Kang, Yan Xia, Chui‐Ping Yang

Published Nov 3, 2025• 3 citations

Abstract

We propose an enhanced entanglement generation scheme in the non-Hermitian system by introducing an ancillary qubit with adjustable driven field to control the target entanglement, making this model more suitable for the switch operation at the quantum interface. Moreover, through adiabatic elimination, the mode of the qubit has been eliminated, and direct coupling between the cavities has been realized. The effective coupling strength between two non-Hermitian microwave cavities can be adjusted as an optimal value to satisfy a specific phase condition that realizes the maximally entangled state on a timescale. To prove the ability of our scheme to improve the performances of entanglement generation in the non-Hermitian system, the numerical simulations are performed based on a model where two microwave cavities are indirectly coupled through a superconducting qubit. It is evident that non-Hermitian cavities can be entangled significantly faster than Hermitian cavities, with the relative speedup increasing significantly as the perturbation is decreased, and the fourth-order exceptional points at J=0 are approached. Last but not least, our scheme has good robustness against parameter errors, crosstalk, and Gaussian white noise and is a feasible scheme for enhanced entanglement generation via approaching to higher-order exceptional points in a non-Hermitian network system.

DOI: 10.1063/5.0296790

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Abstract Open quantum systems are susceptible to losses in information, energy, and particles due to their surrounding environment. One novel strategy to mitigate these losses is to transform them into advantages for quantum technologies through tailored non-Hermitian quantum systems. In this work, we theoretically propose a fast generation of multipartite entanglement in non-Hermitian qubits. Our findings reveal that weakly coupled non-Hermitian qubits can accelerate multiparty entanglement generation by thousands of times compared to Hermitian qubits, in particular when approaching the 2 n -th order exceptional points of n qubits in the P T − symmetric regime. Furthermore, we show that Hermitian qubits can generate GHZ states with a high fidelity more than 0.9995 in a timescale comparable to that of non-Hermitian qubits, but at the expense of intense driving and large coupling constant. Our approach is scalable to a large number of qubits, presenting a promising pathway for advancing quantum technologies through the non-Hermiticity and higher-order exceptional points in many-body quantum systems.

We propose a method to achieve a coherent switch of optomagnonic entanglement in a cavity optomagnonic system with non-Hermitian coupling. The strength of photon-photon and photon-magnon entanglement can be controlled by tuning the relative phase angle of two nanoparticles and optimizing the detuning of two optical modes. We show that the bipartite entanglement is significantly enhanced by selecting a suitable optomagnonics coupling strength in the presence of the exceptional points (EPs). The relative phase not only enhances the entanglement strength but also increases the entanglement domain over a wide range of detuning compared to the Hermitian system. By manipulating the system toward or away from EPs, versatile tunability of the tripartite entanglement, mean photon, and magnon numbers can be achieved. Additionally, the direction of asymmetric transmission can also be well tuned in a highly asymmetric way via non-Hermitian coupling. The study of controlled entanglement may provide the theoretical basis and reference for the research and development of new tunable quantum devices.

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The exploration of the effect of non-Hermitian (NH) in quantum systems is gaining renewed momentum as a result of the recent progress in experiments. It has been indicated that the ability to engineer the orders of exceptional points (EPs) can be fundamental to its applications in quantum control, such as accelerating entanglement generation; however, an initial survey of the interactions between different orders of EPs is still missing. In this work, we try to partially address this issue by employing a non-reciprocally coupled cavity system which can be experimentally realizable with a two-dimensional reconfigurable NH gauged laser array. With deliberate design, our systems display both second and third orders of EPs. The sign of a novel, purely quantum continuous entanglement phase transition is observed, which reveals how multi-EP interactions alter entanglement dynamics across different regimes while maintaining accelerated generation. Our findings reveil the genuinely quantum NH physics of higher-order EPs, which has opened up a new avenue for future investigations of the higher-order degeneracy application and the dynamic phase transitions of quantum systems.